1. Field of Invention
The present invention relates generally to substructures capable of supporting heavy machinery, such as a rotary drilling rig, to traverse and work over ground obstructions. More particularly, the present invention relates to a substructure having at least a pair of ground engaging feet and a pair of telescoping legs and including a pair of articulating pad assemblies that alternatively lift the feet and the pads from the ground and move the feet and pads relative to one another to move the substructure over ground obstructions such as well heads.
2. Background of Invention
Heavy machinery has been supported by a variety of substructures capable of moving over the ground. An early example is the self-propelled platform vehicle disclosed in U.S. Pat. No. 3,754,790 issued to Mappin et al (Mappin '790). The vehicle is described as having two ground engaging sole plates carrying hydraulic rams for raising the vehicle from the ground to enable the vehicle to be advanced by a pair of advancing rams. The vehicle is incrementally walked over the ground by alternating ground contact of the sole plates. A significant disadvantage to the self-propelled vehicle of Mappin '790 is the lack of a means to walk over ground obstructions.
Another example of an alternating ground contact walker is disclosed in U.S. Pat. No. 3,734,220 issued to Smith (Smith '220). The deck or work platform of Smith '220 includes eight legs and a horizontal sliding frame wherein four legs are fixed at the corners of the deck platform and the other four legs are fixed to the corners of the horizontal sliding frame. The deck platform moves over the ground by alternating ground contact of the two sets of legs. While the legs are extensible, it is achieved through a screw jack mechanism capable of biding and failure if not properly maintained. Other disadvantages to the self-propelled platform of Smith '220 are the number of legs in alternating contact with the ground; the use of a horizontal sliding frame at the upper end of the legs; and the lack of a means to breakdown, transport and reassemble the self-propelled platform at desired locations.
The walking tree harvesting machine of U.S. Pat. No. 3,804,137 issued to McColl (McColl '137) addresses the lack of breakdown, transportability and reassembly of the incremental walking substructure of Smith '220. However, the McColl '137 walking tree harvesting machine requires the use of a horizontal sliding frame similar to that of Smith '220 and further lacks the ability to sustain prolonged elevated movement and operations. The incremental walking substructure disclosed in U.S. Pat. No. 5,921,336 issued to Reed (Reed '336) overcomes the disadvantages of the horizontal sliding frame of Smith '220 and McColl '137 by alternating ground contact between the substructure and a plurality of jack pads wherein each jack pad includes an upper section which is in roller contact with a rail attached to a lower section, thereby eliminating the need for a horizontal sliding frame. However, the walking substructure device described in Reed '336 has no means to sustain prolonged elevated movement and operations of the substructure above ground obstructions.